Hydrotreatment of hydrocarbon feeds such as sulphur-containing petroleum cuts is becoming more and more important in refining due to the increasing necessity of reducing the quantity of sulphur in petroleum cuts and to convert heavy fractions to lighter fractions which can be upgraded to fuels. This results partly from an increasing demand for fuels which necessitates conversion of imported crude oils which are becoming poorer in hydrogen and richer in heavy fractions and heteroatoms, among them nitrogen and sulphur, and partly due to the regulations imposed by various countries on commercial fuels. This upgrading implies a relatively large reduction in the molecular weight of the heavy constituents which can be achieved, for example, by means of cracking reactions.
Current catalytic hydrorefining processes use catalysts which can promote the principal reactions used to upgrade heavy cuts, in particular aromatic ring hydrogenation (HAR), hydrodesulphuration (HDS), hydrodenitrogenation (HDN) and other hydroeliminations. Hydrorefining is used to treat feeds such as gasolines, gas oils, vacuum gas oils, and atmospheric or vacuum residues, deasphalted or otherwise. As an example, it is recommended for pre-treating feeds from catalytic cracking and hydrocracking processes. At least one hydrorefining step is normally integrated into each of the known flow sheets for upgrading heavy petroleum cuts. The influence of this prior hydrotreatment on the overall yield and service life of the cracking catalyst and/or hydrocracking catalyst is greater if hydrotreatment catalysts are used which are more active as regards hydrodenitrogenation, hydrodesulphuration and hydrogenation.
The field of the present invention, which is summarised above, is well known to the skilled person. A detailed analysis on this subject can be found in "Oil and Gas Journal, 16.sup.th February 1987, pp. 55 to 66, by Van Kessel et al.
Simple sulphides of group VB or group VIB elements have been described as constituents of hydrorefining or hydroconversion catalysts for hydrocarbon feeds, such as niobium trisulphide described in U.S. Pat. No. 5,294,333. Group VB metals such as niobium are known to be very difficult to sulphurate and conventional sulphuration methods do not generally result in the formation of mixed sulphides but only in simple sulphides or mixtures of simple sulphides. Thus only mixtures of simple sulphides comprising at least one group VB element and one group VIB element have been able to be tested as constituents of hydrorefining or hydroconversion catalysts for hydrocarbon feeds, such as in U.S. Pat. No. 4,910,181 or U.S. Pat. No. 5,272,994.